CARADOCIAN CYSTIDEA FROM GIRVAN. 



453 



marked 6l [-2j. In pi. 12, "H" [=6] is attached to plate 7; "Z2" [ = 5] to 

 plate 6 ; "1 5" [ = 7] to plate 8; "/4" [ = 8] to plate 9; the other plates are not 

 specially numbered. Therefore, though pi. 12 is more correct as regards the basals 

 2 and 3, it is quite astray as regards plates 6, 7, 8, 9. It is the more necessary to 

 note this, since the erroneous numbering has already found its way into the text-books 

 (Broili's "Zittel," 1910, p. 187). 



§ 369. I am much indebted to Dr Edwin Kirk for having recently (1911, p. 21) 

 called attention to the fact that "the analysis of the theca and the figures of Pleuro- 

 cystis as given by Jaekel and Bather are inaccurate in several important features." 

 His first criticism, concerning plates 1 to 4, has already been dealt with in part (§ 367). 

 He says " plates 1 and 4 as given by them should be split vertically and portions united 



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Fig. 61. 



Text-fig. 60.— Amdjsis of PlcurocystisJilitextM, after Jaekel. This diagram is based on Jakkel's diagram (1899), but is 

 modified therefrom by the spacing out of the plates, by the transposition of all the plates here shown on the left of the 

 periproct from the right-hand side of his diagram, and by the numbering of the plates according to the system followed 

 in this memoir (cf. text-figs. 36 and 37). In this diagram, as in the following one, the plates are spaced so that 

 those which in the fossil lie on the same meridians here also come in vertical series. It is not possible to protract in a 

 single plane those plates which are sharply bent round the margin of the theca {e.g. 12 and 14), and in the case of certain 

 basals this difficulty has in part been overcome by splitting them along the marginal meridian. 



Text-fig. 61. — Analysis of Plcurocystis filitexta, original. This is intended to supersede the analysis in the "Treatise on 

 Zoology" {1900, fig. xxxiv. 1), which was incorrect in some points. The brachioles spring, on the right hand from 

 plate 20, on the left hand from the curve above plates 22 and 17. 



with 2 and 3." Except for the rather inexact use of the word " vertical," I accept this 

 correction so far as my own diagram is concerned. Since I have not seen the original 

 of Dr Jaekel's pi. 12, f. 3, I express no opinion as to its correctness ; his f. 6 is not 

 so open to Dr Kirk's criticism, and agrees fairly well with the specimen in these points 

 (see § 469). Neither would I venture to criticise Dr Kirk's drawing of a specimen of 

 P. filitexta at the University of Chicago (his pi. 3, f. 3) ; I will only say that in 

 specimens of that species in the British Museum (E7535, E7683, E15923, E 15924), 

 as also of P. squamosa (E 15925), and indeed of all the Canadian species, the lower 

 margin of plate 6 is about equally shared by plates 1 and 2, so that plate 1 is five-sided 

 and the suture 1|2 is not continuous with the suture 5|6. The same point is fairly 



